It is a bit longwinded admittedly, I just double checked the page and they seem to be having some problems tonight, if you go down the page and click on the silver driver download it will bring another page up, on the box for this, it seems squashed for some reason click on the company name you see, will take you to their page and you can download it for free. Don't know what is wrong with the site, when I checked earlier took me straight to it.

Click on that link, think this is the usb driver you want, will take you straight to it with no hassles, at the bottom left of the description is the download box, just hit it and you are there, the next screen shows a couple of mirrors you can choose from if necessary. If this is not the exact one for you then just type it in the search box on this site and it will bring it up.